In general terms, a photodetector is a device that generates an electrical current when illuminated. Photodetectors can respond differently depending on the wavelength of the illumination, depending on the materials used to construct the photodetector.
J-aggregates are clusters of coherently-coupled molecular dyes. Their intense absorptions and ultrafast excited state lifetimes make them useful as light sensitizers for film photography, and for such potential applications as color-selective CCD operations and biomimetic color imaging. However, application of J-aggregates in optoelectronic devices has lagged, due to the difficulty of controlling the formation of aggregates and the low charge carrier mobility of many J-aggregates in solid state.